The therapies of deep-brain stimulation (DBS) and auditory neuron stimulation have gained significantly clinical popularity over the past decades. The former has significant applications in the treatment of a variety of brain-controlled disorders, including movement disorders, while the latter has applications in the treatment of hearing impairment.
Generally, such treatments involve identifying a corresponding physiological target to be stimulated, surgically drilling a burr hole in the patient's skull or temporal bone to create an access to the corresponding physiological target, placing an electronic device in the corresponding physiological target through the drilled burr hole, and then applying appropriate stimulation signals through the implanted electrode device to the physiological target.
The placement portion of the treatment, involving stereotactic neurosurgical methodology, is very critical, and has been the subject of much attention and research. In particular, finding the deep brain target and then permanently placing the electrode lead so that it efficiently stimulates such target is very important.
Stereotactic neurosurgery is a field of neurosurgery in which a probe is advanced through a burr hole to a target of interest by means of a mechanical device attached to the skull with aiming based on pre-operative images. The probe may be a biopsy needle or an implantable device, but it is geometrically rigid, so that its tip, or working end portion, can be brought to a target of interest specified on a pre-operative image, by means of a geometrical calculation. For the past decade, the field has been advancing from the imposition of large, classical metal frames, which encompass the entire head of a patient, to the attachment of small platforms placed only over an entry site to reduce patient discomfort, facilitate surgical access, allow multiple targeting during one surgery via multiple platforms, and reduce procedure time, while maintaining the same level of accuracy.
Classical metal frames are designed for approaching one target at a time with an unrestricted entry point towards the deep target by employing the principle that the target is at the center of a sphere. Because of the long trajectories experienced by the probe when it goes through from a starting point, which is normally outside of the head of the patient, to target areas deep inside the head of the patient, both accuracy and patient comfort are challenged by the demands of surgeries for deep brain stimulation (DBS) in which the patients are awake throughout the lengthy surgery procedure (normally about 5-8 hours).
During the last few years, microplatforms, such as a NEXFRAME™ (Image-Guided Neurologics, Inc, Melbourne, Fla.) and a microtargeting platform (FHC Inc, Bowdoinham, Me.), also known as a STarFix™ platform, have become available as replacements for the classical frames for DBS stereotactic surgery.
It is understood that the NEXFRAME™ platform requires the attachment of bone-implanted fiducials, the subsequent acquisition of a preoperative tomogram, and intraoperative optical tracking to aim a probe at its target. However, there are problems regarding geometrically stability, limited space for access to the burr hole and surgical manipulation once the tower is mounted, the time consuming process of aiming, and the difficulty of locking on the target. Access to the burr hole is crucially important for the purpose of stopping bleeding from the bone cavity, dura, and the surface of the cortex during the procedure. Aiming is achieved by watching a guiding icon on the screen of the intraoperative tracking system, while adjusting the orientation of the platform. When the icon indicates a correct trajectory, the platform must be locked into place with one hand, while it is held at the correct trajectory with the other. The trajectory is two-dimensional, meaning that there are two mutually perpendicular angular adjustments required, each of which must be set simultaneously for the correct trajectory. Finding the correct trajectory via the guiding icon is time consuming because of the difficulty of making fine adjustments of one angle of the approach without changing the other angle. A further difficulty with this aiming procedure is maintaining both angles of the correct trajectory while locking the device on target. The locking step can be especially frustrating, because, if either angle is changed inadvertently during locking, as revealed by the guiding icon, the device must be unlocked and the adjustment started from the beginning. Typically several iterations are required, resulting in wasted operating time.
It is understood the other alternative, the STarFix™, also requires the attachment of bone-implanted fiducials and the subsequent acquisition of a preoperative tomogram, but it does not require intraoperative optical tracking for aiming. Instead the STarFix™ is custom-made for each patient based on a pre-operative tomogram and the surgeon's identification of the entry point and the target on that tomogram. The device arrives at the operating suite pre-aimed with no adjustment required intraoperatively. It is a one-piece rigid plastic block having a cylindrical hole that accommodates the probe, supported by a plurality of legs, each of which attaches to a base that is implanted in the skull. Fiducial markers are attached to these same bases before the pre-operative image is acquired and discarded after imaging. The shape of the STarFix™ provides far greater access to the burr hole, but its paramount advantage is that it is “pre-aimed”, obviating the aiming procedure required by the NEXFRAME™. An additional benefit, but one that does not directly affect accuracy or operating time is that the expense of an intraoperative tracking system is avoided. One of its disadvantages relative to the NEXFRAME™ is that the patient must wait between the acquisition of the tomogram and the delivery of the STarFix™. Currently, this interval ranges from two to four days. The wait between image acquisition and surgery is a disadvantage inherent to the production of the customized STarFix™, but the primary disadvantages of the NEXFRAME™ are a consequence only of its mechanical design.
Therefore, a heretofore unaddressed need still exists in the art to address the aforementioned deficiencies and inadequacies.